1. Field of the Invention
This invention relates generally to satellite communication systems. In particular, this invention relates to a transcoder for efficiently converting satellite data encoded in one satellite modulation scheme to another.
2. Related Art
From the inception of convenient direct broadcast satellite (“DBS”) services such as DBS service providers DirectTV® and DISH Network® in the United States and similar services around the world, there has been a tremendous growth in the number of DBS subscribers. As more subscribers enroll in DBS services, DBS service providers are offering a greater number of services including, but not limited to, addition pay-per view, high definition Television (“HDTV”), broadband Internet, satellite radio transmission, and other bandwidth-intensive services. As such, DBS providers require higher throughput to offer these bandwidth-intensive services to their growing number of subscribers.
In the past, DBS service providers typically utilized a digital modulation scheme known as Quadrature Phase Shift Keying (“QPSK”) to modulate their DBS signals. QPSK allows for low signal-to-noise ratios (known as “S/N” or “SNR”) with relatively high throughput data communication between a broadcasting satellite and a DBS set-top module (i.e., a “set-top box”) in the premises of a subscriber.
FIG. 1 is a block diagram of an example prior art implementation of a typical DBS service connection 100 between a broadcasting DBS satellite 102 and a QPSK DBS set-top module 104 located at the premises 106 of a subscriber. In FIG. 1, the subscriber has the QPSK DBS set-top module 104, an antenna 108, low noise block downconverter (“LNB”) 110, and video monitor 112 located within the subscriber premises 106. The subscriber premises 106 may be either a place of business or a personal residence. The LNB 110 may be any device that converts a whole band (or “block”) of frequencies to a lower band of frequencies. The QPSK DBS set-top module 104 may be any generally known QPSK DBS set-top box similar to the set-top boxes produced by multiple manufactures for both DirectTV® and DISH Network®, or other similar type of DBS service provider. The video monitor 112 may be any device capable of receiving the information delivered by the QPSK DBS set-top module 104. Examples of the video monitor 112 may include a television set, a television monitor (without a television receiver), a computer monitor, and/or a video recording device. The antenna 108 may be any device capable of receiving transmissions from DBS satellite 102. Examples of the antenna 108 may include an 18-inch reflector antenna (typically know as a “dish antenna”) or any other type of antenna such as a phased array, patch, and/or active or passive antenna.
As an example of operation, the DBS satellite 102 transmits a signal to the satellite antenna 108 via transmission path 114. The antenna 108 receives the signal and passes the received signal to the LNB 110 that down converts the received signal to a lower frequency band. The LNB 110 then passes, via signal path 116, the down-converted signal to the QPSK set-top module 104. The QPSK set-top module 104 then demodulates and decodes the down-converted signal and produces an output signal that is passed to the video monitor 112 via signal path 118.
Unfortunately, presently available QPSK transmission schemes will not be able to support the greater bandwidth-intensive services desired by the DBS services providers. As a result, DBS service providers have been experimenting with new transmission schemes to try to support the greater bandwidth-intensive services. Some of these new transmission schemes have included utilizing Turbo Codes, which achieve near-capacity performance on the additive white Gaussian noise channel.
In response, there is presently a movement to switch DBS transmissions from the old QPSK transmission schemes to new transmission schemes based on 8-PSK Turbo Coding, which may increase the throughput for advanced DBS services by as much as 50% over present commercial satellite links, while still being compatible with the existing DBS infrastructure. Generally, this approach provides DBS service providers with an efficient method of increasing throughput over the existing satellite infrastructures while providing new services for their customers.
Unfortunately, switching transmission schemes will typically force established DBS subscribers to upgrade their reception equipment because the old QPSK set-top modules cannot decode the new 8-PSK Turbo Coded transmissions. Therefore, there is a need for a system that allows established DBS subscribers to receive the new 8-PSK Turbo Coded transmission with their old QPSK set-top modules (also known as a “legacy set-top module”).